1Question 1
2 marks
A wave has a frequency of 50 Hz and a wavelength of 4 m. Calculate the wave speed. (2 marks)
Model answer
v = fλ = 50 × 4 = 200 m/s.
Mark scheme
- Uses speed = frequency × wavelength1 mark
- 200 m/s1 mark
WASSCE SHS
WASSCE Physics: Waves
Wave speed equals frequency times wavelength. Frequency is how many waves pass a point each second. Wavelength is the distance from one crest to the next.
The idea
A wave transfers energy without transferring the material itself, once the wave has passed. In a transverse wave the oscillation is perpendicular to the direction the wave travels. Light and a wave on a string are transverse. In a longitudinal wave the oscillation is along the direction of travel, as compressions and rarefactions. Sound in air is longitudinal. Both kinds obey wave speed = frequency × wavelength, with speed in metres per second when frequency is in hertz and wavelength is in metres.
The amplitude is the maximum displacement from the rest position. It is related to energy, not to speed. A louder sound has a larger amplitude. It does not travel faster in the same air. A higher pitch is a higher frequency, not a larger amplitude. When you calculate, convert a wavelength given in centimetres into metres before you multiply, or keep every length in centimetres and say so. Mixing cm and m silently is a factor of 100.
What earns the marks
The formula line is a mark, and the unit is part of the final mark. Hertz times metres is metres per second. Do not call sound transverse. Do not call light longitudinal. Amplitude and frequency answer different questions. If the question asks why a note is louder, talk about amplitude. If it asks why the note is higher, talk about frequency.
Practice questions
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
2Question 2
4 marks
(a) State one example of a transverse wave and one example of a longitudinal wave. (2 marks)
(b) What is the difference in the way the particles move? (2 marks)
Model answer
(a) Light is transverse. Sound in air is longitudinal.
(b) In a transverse wave the particles oscillate at right angles to the direction of travel. In a longitudinal wave they oscillate along the direction of travel.
Mark scheme
- A transverse example, such as light or a water wave on the surface1 mark
- A longitudinal example, such as sound in air1 mark
- Transverse: oscillation perpendicular to travel1 mark
- Longitudinal: oscillation parallel to travel1 mark
3Question 3
2 marks
A louder sound of the same pitch is made. State what has changed and what has stayed the same. (2 marks)
Model answer
The amplitude has increased. The frequency has stayed the same, because the pitch is the same.
Mark scheme
- Amplitude increases1 mark
- Frequency is unchanged1 mark
Practise Physics with Anna
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
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